The present invention relates to the electrode art. It finds particular application in conjunction with carbon electrodes for use in peracetic acid detectors and will be described with particular reference thereto. It is to be appreciated, however, that the invention will also find application in conjunction with carbon-based electrodes for use in other electrochemical applications.
Heretofore, in liquid-based sterilization systems, a premeasured dose of a strong oxidant antimicrobial agent, such as peracetic acid or reagents which react to form peracetic acid, hydrogen peroxide, chlorides, hydrochlorite, and other strong oxidants, was added to each disinfection or sterilization cycle. Strong oxidants react with the microbes and other contaminants that may be in the system. In medical applications, a blood residue is a strong oxygen scavenger. To determine whether an appropriate concentration of the antimicrobial agent was maintained in solutions for an appropriate time, biological and chemical indicators were typically placed with the items to be disinfected or sterilized in the processor. After the cycle, these indicators were incubated and examined, colorimetrically examined, or otherwise examined to provide a pass/fail indication of the success of the disinfection or sterilization cycle. While it would be advantageous to provide a real time parametric monitoring of the antimicrobial agent concentration, cost effective, accurate, reliable, and long-lived monitors have proved elusive.
One particular promising electrochemical sensor includes three electrodes, a working electrode, a counter electrode, and a reference electrode which are emersed in this liquid to be monitored. Metallic counter electrodes and silver/silver chloride reference electrodes which can be immersed in the strong oxidants for extended periods are available at a relatively reasonable cost. However, the ideal glassy carbon working electrode tends to be fragile, expensive, and has a relatively short working life.
Prior art carbon electrodes typically include a short rod of a glassy carbon, a brittle fragile material. A glassy carbon rod is commonly interfaced electrically with a metallic electrode rod using a graphite or other conductive grease. The peripheral surface of the carbon rod, the electrode rod, and the grease interface is surrounded by a plastic sheath, e.g., a heat shrunk plastic sheath. The face of the glassy carbon electrode is polished, typically hand polished. Unfortunately, the plastic sleeve does not adhere tightly to the carbon electrode under all normal operating conditions. For example, when mounted in a sealed fitting, the plastic sleeve tends to separate from the carbon allowing the monitored solution to pass in between. This provides both an escape path for the conductive graphite grease and an entrance path for the analyzed solution to degrade the grease and the metal electrode. Further, fluid access along the side of the electrode changes the effective surface area of the electrode, hence its output characteristics. When the plastic ceases to hold the carbon electrode firmly against the grease and the metal electrode, the electrical signal transmission characteristics are altered and eventually totally interrupted.
Glassy carbon electrodes are used in other electrochemical analysis and other processes. In some, the carbon itself is used as the electrode. In others, the carbon is used as a carrier for a different electrode material, such as mercury. In these other applications, particularly applications in which the carbon electrode is handled manually, the delicacy of the electrodes, their cost, and short working life are again significant drawbacks.
In accordance with the present invention, a new and improved carbon electrode, parametric sensing system, and disinfectant/sterilizer with improved parametric monitoring are provided.
In accordance with one aspect to the present invention, a glassy carbon electrode is provided. A compressible insulating sleeve surrounds a glassy carbon rod. The compressible insulating sleeve compresses at a pressure lower than a compressive pressure at which the glassy carbon rod fractures. A ductile sleeve surrounds the insulating sleeve. The ductile sleeve is compressed, compressing the insulating sleeve and providing a fluid tight seal between the ductile sleeve, the insulating sleeve, and the glassy carbon rod.
In accordance with another aspect of the present invention, an electrochemical analyzer cell is provided. An electrochemical analysis chamber defines a fluid receiving reservoir. A plurality of measurement electrodes is disposed in the reservoir to be in electrical contact with solutions received in the reservoir. At least one of the electrodes being a glassy carbon electrode supported and sealed in a metallic sleeve. An analysis control system connected with the electrodes applies at least the currents to the electrodes and reads currents which are indicative of a concentration of a target anolyte.
In accordance with yet another aspect of the present invention, a disinfectant/sterilant system is provided. A chamber receives an item to be disinfected or sterilized. A pump pumps a peroxyacetic acid antimicrobial solution into the chamber. An electrochemical analysis chamber is fluidicly connected to receive the peracetic acid solution flowing to the chamber. The electrochemical analysis chamber defines a fluid receiving reservoir. A plurality of measurement electrodes are disposed in the reservoir to be in electrical contact with solutions received in the reservoir. At least one of the electrodes is a glassy carbon electrode supported and sealed in a metallic sleeve. An analysis control system is connected with the electrodes to apply at least voltages to the electrodes and read currents which are indicative of peroxyacetic acid concentration.
In accordance with yet another aspect of the present invention, an electrochemical method is provided. A glassy carbon rod is surrounded with an insulating sleeve which, in turn, is surrounded by ductile metallic sleeve. The metallic sleeve is compressed forming a fluid tight compression seal with the insulating sleeve and the glassy carbon rod. An electrical connection is made with the glassy carbon rod which compensates for thermal expansion of the metallic sleeves. The electrical connection is connected with an electrochemical analysis system. A face of the glassy carbon rod is immersed into a fluid to be analyzed.
One advantage of the present invention is that it facilitates parametric monitoring of peroxyacetic acid concentration.
Another advantage of the present invention resides in a more durable and longer lived carbon electrode.
Another advantage of the present invention resides in its cost efficiency.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.